In a method of making an optical fiber product, the present invention relates to a technique in which a control step is provided between the time at which a drawing step is completed and the time at which its subsequent processing step is started, and the operating time of the control step is optimally regulated in relation to the ambient temperature during this step.
The conventional method of making an optical fiber product includes, at least, a preform manufacturing step of making a preform for optical fiber by means of a so-called VAD (vapor phase axial deposition) technique or the like, a drawing step of drawing thus obtained preform so as to yield a coated optical fiber, and a processing step of making a ribbon-type optical fiber or an optical fiber code by utilizing thus obtained coated optical fiber, whereby a desired optical fiber product has been made in consequence of all these steps. In this specification, the coated optical fiber refers to a light guide member which is obtained by the above-mentioned drawing step and comprises, as shown in FIG. 2, a glass fiber 3 constituted by a core having a predetermined refractive index and a cladding which is disposed around the outer periphery of the core and has a refractive index lower than that of the core, and a primary coating layer 40 made of a UV-curing resin or the like disposed around the outer periphery of the glass fiber 3. As the prior art relating to the above-mentioned preform manufacturing step, for example, U.S. Pat. No. 4,367,085 discloses the VAD technique. The prior art relating to the above-mentioned drawing step is disclosed in U.S. Pat. No. 4,123,242, for example. As the prior art relating to the above-mentioned processing step, U.S. Pat. No. 5,561,730 discloses a configuration of a ribbon-type optical fiber.
In the above-mentioned method of making an optical fiber product, after the coated optical fiber is wound around a reel 1 (first winding member) once (after the completion of the drawing step), the subsequent processing step is performed while the coated optical fiber is directly rewound around another bobbin or after the coated optical fiber is further temporarily rewound around a bobbin (second winding member) which is different from the above-mentioned reel.
For example, in the drawing apparatus shown in FIG. 1, the glass fiber 3 (see FIG. 2) constituted by the core and the cladding is obtained when a tip portion of an optical fiber preform 10 softened by a heating oven 11 is drawn into the direction of depicted arrow S1, while a predetermined tension is applied thereto, and is wound around the reel 1 rotating in the direction indicated by depicted arrow S2. At this time, a coating apparatus 12 applies a resin to the outer periphery of the glass fiber 3, and the primary coating layer 40 made of the UV-curing resin, which is cured in a curing furnace 13, is subsequently formed. Accordingly, in this drawing step, a coated optical fiber 4, in which the primary coating layer 40 is formed on the outer periphery of the glass fiber 3, is wound around the reel 1.
The processing step performed after the above-mentioned drawing step includes, for example, a step of making a ribbon-type optical fiber 6 shown in FIG. 3. In this step, first, the coated optical fiber 4 wound around the reel 1 in consequence of the drawing step is divisionally wound around a plurality of bobbins simultaneously. Thereafter, a plurality of coated optical fibers 4 respectively wound around the bobbins are collectively covered with a coating layer 60 made of a UV-curing acrylate resin or the like in the state where they are arranged horizontally, whereby the ribbon-type optical fiber 6 shown in FIG. 3 is obtained.
Also, the above-mentioned processing step includes a step of yielding a colored coated optical fiber 5 in which, as shown in FIG. 4, a coloring layer 50 made of a UV-curing acrylate resin containing a pigment or the like is formed on the outer periphery of the optical fiber bundle 4 wound around the reel 1. This colored coated optical fiber 5 can also be employed in the ribbon-type optical fiber 6 shown in FIG. 3. Specifically, the colored coated optical fibers 5 are collectively covered with the coating layer 60 made of a UV-curing acrylate resin or the like in the state where they are arranged horizontally, whereby the ribbon-type optical fiber 6 shown in FIG. 5 is obtained.
Further, the above-mentioned processing step 15 includes a step of yielding a single-filament optical fiber code 7 in which, as shown in FIG. 6, a coating layer 70 made of nylon or the like is disposed around the outer periphery of the coated optical fiber 4, while the coated optical fiber 4 is being rewound from the reel 1.
In addition, the above-mentioned processing step includes a step of rewinding the coated optical fiber 4, which has been wound around the reel 1 in the above-mentioned drawing step, simply around a single bobbin different from the reel 1 or divisionally around a plurality of bobbins.
In the conventional method of making an optical fiber product, no control has been made at all with respect to the time for starting the processing step (including the step of rewinding the coated optical fiber 4 around the second winding member) that is effected for forming the coloring layer 50, the casing 60, or the casing 70 and the like after the completion of the drawing step (including the step of winding the coated optical fiber 4 around the first winding member).
In the optical fiber product (the ribbon-type optical fiber 6, single-filament optical fiber code 7, colored coated optical fiber 5, coated optical fiber 4 rewound around another bobbin from the reel 1, or the like) thus made by the conventional manufacturing method, there have been cases where delamination (8 indicating a delaminated portion in FIG. 7) locally occurs between the glass fiber 3 and the primary coating layer 40 disposed around the outer periphery thereof, thereby increasing transmission loss. Also, this delamination has been causing the strength to deteriorate.
Similarly, in the ribbon-type optical fiber 6 (see FIG. 5) obtained when a plurality of colored coated optical fibers 5 each having the coloring layer 50 made of a UV-curing resin containing a coloring pigment formed around the outer periphery of the coated optical fiber 4 are collectively covered with the coating layer 60 made of a UV-curing resin while being arranged horizontally, there have been cases, as shown in FIG. 8, where color delamination (9 indicating a color-delaminated portion in FIG. 8) occurs when the coating layer 60 is removed therefrom.
The locally generated delamination has mainly been studied from the viewpoint of improving the composition of the primary coating layer so as to increase its bonding force, whereas the color delamination has been studied from the viewpoint of improving the coloring layer. In either case, however, the above-mentioned problem has not been solved.
Hence, it is an object of the present invention to provide a method of making an optical fiber product, which efficiently restrains the primary coating layer or ink (coloring layer) of the resulting optical fiber product from delaminating.
Specifically, the method of making an optical fiber product according to the present invention comprises, at least, a drawing step (first step) of winding around a first winding member (e.g., reel) a coated optical fiber in which a primary coating layer made of a UV-curing resin or the like is formed around the outer periphery of a glass fiber having a core and a cladding; a processing step (second step) of rewinding around a second winding member (bobbin), which is different from the first winding member, the coated optical fiber wound around the first winding member; and a control step (third step), provided between the drawing step and the processing step, of holding thus obtained coated optical fiber in an atmosphere with a mean temperature T ( greater than 0xc2x0 C.) for a predetermined time.
In particular, the control step provided between the above-mentioned drawing and processing steps is characterized in that, when the coated optical fiber is held in the atmosphere with a mean temperature T ( greater than 0xc2x0 C.), the holding time for the coated optical fiber is set such that an interval of at least 30,000/T2 (hr) is secured between the time at which the coated optical fiber is completely wound around the first winding member and the time at which the coated optical fiber is started to be rewound around the second winding member.
Also, in this specification, the optical fiber product encompasses, at least, the coated optical fiber (see FIG. 2) comprising a glass fiber having a core and a cladding and a primary coating layer made of a UV-curing resin or the like disposed around the outer periphery of the glass fiber; the ribbon-type optical fiber (see FIG. 3) obtained when a plurality of horizontally arranged optical fibers are collectively covered with a resin; the colored coated optical fiber (see FIG. 4) obtained when a resin containing a coloring pigment is disposed around the outer periphery of a coated optical fiber; and the ribbon-type optical fiber (see FIG. 5) obtained when a plurality of horizontally arranged colored coated optical fibers are collectively covered with a resin; and the optical fiber code (see FIG. 6) obtained when a coating layer made of nylon or the like is disposed around the outer periphery of the coated optical fiber.
Accordingly, the above-mentioned processing step includes at least one of a step of simply rewinding a coated optical fiber, which has been wound around a reel, around a bobbin different from the reel; a step of divisionally rewinding a coated optical fiber, which is obtained by the drawing step (wound around a reel), around a plurality of bobbins simultaneously and then collectively covering a plurality of coated optical fibers thus respectively wound around the bobbins with a coating layer made of a UV-curing resin in the state where they are horizontally arranged, so as to yield a ribbon-type optical fiber; a step of rewinding a coated optical fiber, which is obtained by the drawing step, around a bobbin and simultaneously forming a coloring layer on the outer periphery of the coated optical fiber; and a step of rewinding a coated optical fiber, which is obtained by the drawing step, around a bobbin and simultaneously yielding a single-filament optical fiber code in which a coating layer made of nylon or the like is disposed around the outer periphery of the coated optical fiber.
Further, in the method of making an optical fiber product according to the present invention, when the above-mentioned processing step (second step) includes the step of rewinding a coated optical fiber, which has been wound around the first winding member, around the second winding member and simultaneously providing a coloring layer on the surface of the coated optical fiber, the holding time for the coated optical fiber in the control step (third step) is set such that the interval between the time at which the drawing step is completed (the time at which the coated optical fiber is completely wound around the reel) and the time at which the processing step is started (the time at which the coated optical fiber is started to be rewound around the bobbin) is not longer than 210,000/T2 (hr). Here, T ( greater than 0xc2x0 C.) is a mean atmospheric temperature of a place where the coated optical fiber wound around the reel is held after the completion of the drawing step.
Also, it is preferred that the mean atmospheric temperature of the place where the coated optical fiber wound around the reel is held be higher than 0xc2x0 C. but not exceeding 60xc2x0 C.